{"id":35396,"date":"2019-10-31T22:04:04","date_gmt":"2019-10-31T19:04:04","guid":{"rendered":"https:\/\/prohoster.info\/blog\/uyazvimosti-v-tcp-stekah-linux-i-freebsd-privodyashhie-k-udalyonnomu-otkazu-v-obsluzhivanii\/"},"modified":"2019-10-31T22:04:04","modified_gmt":"2019-10-31T19:04:04","slug":"uyazvimosti-v-tcp-stekah-linux-i-freebsd-privodyashhie-k-udalyonnomu-otkazu-v-obsluzhivanii","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/news\/uyazvimosti-v-tcp-stekah-linux-i-freebsd-privodyashhie-k-udalyonnomu-otkazu-v-obsluzhivanii","title":{"rendered":"Zranitelnosti v TCP z\u00e1sobn\u00edc\u00edch Linuxu a FreeBSD, kter\u00e9 vedou k vzd\u00e1len\u00e9mu odm\u00edtnut\u00ed slu\u017eby","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"

Spole\u010dnost Netflix odhalila<\/a><\/noindex> n\u011bkolik kritick\u00fdch zranitelnost\u00ed<\/a><\/noindex> v TCP stac\u00edch Linuxu a FreeBSD, kter\u00e9 umo\u017e\u0148uj\u00ed vzd\u00e1len\u011b iniciovat p\u00e1d j\u00e1dra nebo vyvolat nadm\u011brnou spot\u0159ebu prost\u0159edk\u016f p\u0159i zpracov\u00e1n\u00ed speci\u00e1ln\u011b vytvo\u0159en\u00fdch TCP paket\u016f (packet-of-death). Probl\u00e9my jsou zp\u016fsobeny<\/a><\/noindex> chybami v obsluh\u00e1ch maxim\u00e1ln\u00ed velikosti bloku dat v TCP paketu (MSS, Maximum Segment Size) a mechanismu voliteln\u00e9ho potvrzen\u00ed spojen\u00ed (SACK, TCP Selective Acknowledgement).<\/p>\n

  • CVE-2019-11477<\/a><\/noindex> (SACK Panic) \u2014 probl\u00e9m se objevuje v j\u00e1drech Linux od verze 2.6.29 a umo\u0148uje zp\u016fsobit p\u00e1d (panic) j\u00e1dra zasl\u00e1n\u00edm s\u00e9rie SACK paket\u016f v d\u016fsledku p\u0159ete\u010den\u00ed celo\u010d\u00edseln\u00e9 hodnoty v zpracovateli. K \u00fatoku sta\u010d\u00ed nastavit pro TCP spojen\u00ed hodnotu MSS na 48 bajt\u016f (doln\u00ed limit, nastavuje velikost segmentu na 8 bajt\u016f) a odeslat sekvenci ur\u010dit\u00e9m zp\u016fsobem sestaven\u00fdch SACK paket\u016f.\n

    Jako obch\u00e1zen\u00ed ochrany lze vypnout zpracov\u00e1n\u00ed SACK (napsat 0 do \/proc\/sys\/net\/ipv4\/tcp_sack) nebo blokovat<\/a><\/noindex> spojen\u00ed s n\u00edzk\u00fdm MSS (funguje pouze p\u0159i nastaven\u00ed sysctl net.ipv4.tcp_mtu_probing na 0 a m\u016f\u017ee naru\u0161it fungov\u00e1n\u00ed n\u011bkter\u00fdch norm\u00e1ln\u00edch spojen\u00ed s n\u00edzk\u00fdm MSS);<\/p>\n

  • CVE-2019-11478<\/a><\/noindex> (SACK Slowness) \u2014 vede k naru\u0161en\u00ed funkce mechanismu SACK (p\u0159i pou\u017eit\u00ed j\u00e1dra Linux verze ni\u017e\u0161\u00ed ne\u017e 4.15) nebo k nadm\u011brn\u00e9 spot\u0159eb\u011b zdroj\u016f. Probl\u00e9m se objevuje p\u0159i zpracov\u00e1n\u00ed speci\u00e1ln\u011b konstruovan\u00fdch SACK paket\u016f, kter\u00e9 lze pou\u017e\u00edt k fragmentaci fronty pro op\u011btovn\u00e9 odes\u00edl\u00e1n\u00ed (TCP retransmission). Ochrann\u00e9 obchvaty jsou podobn\u00e9 p\u0159edchoz\u00ed zranitelnosti;\n
  • CVE-2019-5599<\/a><\/noindex> (SACK Slowness) \u2014 umo\u017e\u0148uje vyvolat fragmentaci mapy odeslan\u00fdch paket\u016f p\u0159i zpracov\u00e1n\u00ed speci\u00e1ln\u00ed sekvence SACK v r\u00e1mci jednoho TCP spojen\u00ed a vyvolat vykon\u00e1v\u00e1n\u00ed v\u00fdpo\u010detn\u011b n\u00e1ro\u010dn\u00e9 operace proch\u00e1zen\u00ed seznamu. Probl\u00e9m se objevuje ve FreeBSD 12 s mechanismem detekce ztr\u00e1ty paket\u016f RACK. Jako ochrann\u00e9 opat\u0159en\u00ed lze zak\u00e1zat modul RACK;\n
  • CVE-2019-11479<\/a><\/noindex> \u2014 \u00fato\u010dn\u00edk m\u016f\u017ee v j\u00e1d\u0159e Linux vyvolat rozd\u011blen\u00ed odpov\u011bd\u00ed na n\u011bkolik TCP segment\u016f, z nich\u017e ka\u017ed\u00fd obsahuje pouze 8 bajt\u016f dat, co\u017e m\u016f\u017ee v\u00e9st k podstatn\u00e9mu n\u00e1r\u016fstu provozu, zv\u00fd\u0161en\u00ed z\u00e1t\u011b\u017ee CPU a zablokov\u00e1n\u00ed komunika\u010dn\u00edho kan\u00e1lu. Jako ochrannou metodu se doporu\u010duje blokovat<\/a><\/noindex> spojen\u00ed s n\u00edzk\u00fdm MSS.\n<\/ul>\n

    V j\u00e1d\u0159e Linuxu byly probl\u00e9my vy\u0159e\u0161eny ve verz\u00edch 4.4.182, 4.9.182, 4.14.127, 4.19.52 a 5.1.11. Oprava pro FreeBSD je dostupn\u00e1 ve form\u011b patche<\/a><\/noindex>. V distribuc\u00edch byly vyd\u00e1ny aktualizace bal\u00ed\u010dk\u016f s j\u00e1drem pro Debian<\/a><\/noindex>, RHEL<\/a><\/noindex>, SUSE\/openSUSE<\/a><\/noindex>. Oprava je v procesu p\u0159\u00edpravy v Ubuntu<\/a><\/noindex>, Fedora<\/a><\/noindex> a Arch Linux<\/a><\/noindex>.<\/p>\n

    <\/a><\/noindex><\/p>\n

    Zdroj: opennet.ru<\/a><\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

    \u041a\u043e\u043c\u043f\u0430\u043d\u0438\u044f Netflix \u0432\u044b\u044f\u0432\u0438\u043b\u0430 \u043d\u0435\u0441\u043a\u043e\u043b\u044c\u043a\u043e \u043a\u0440\u0438\u0442\u0438\u0447\u0435\u0441\u043a\u0438\u0445 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439 \u0432 TCP-\u0441\u0442\u0435\u043a\u0430\u0445 Linux \u0438 FreeBSD, \u043a\u043e\u0442\u043e\u0440\u044b\u0435 \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0442 \u0443\u0434\u0430\u043b\u0451\u043d\u043d\u043e \u0438\u043d\u0438\u0446\u0438\u0438\u0440\u043e\u0432\u0430\u0442\u044c \u043a\u0440\u0430\u0445 \u044f\u0434\u0440\u0430 \u0438\u043b\u0438 \u0432\u044b\u0437\u0432\u0430\u0442\u044c \u0447\u0440\u0435\u0437\u043c\u0435\u0440\u043d\u043e\u0435 \u043f\u043e\u0442\u0440\u0435\u0431\u043b\u0435\u043d\u0438\u0435 \u0440\u0435\u0441\u0443\u0440\u0441\u043e\u0432 \u043f\u0440\u0438 \u043e\u0431\u0440\u0430\u0431\u043e\u0442\u043a\u0435 \u0441\u043f\u0435\u0446\u0438\u0430\u043b\u044c\u043d\u043e \u043e\u0444\u043e\u0440\u043c\u043b\u0435\u043d\u043d\u044b\u0445 TCP-\u043f\u0430\u043a\u0435\u0442\u043e\u0432 (packet-of-death). \u041f\u0440\u043e\u0431\u043b\u0435\u043c\u044b \u0432\u044b\u0437\u0432\u0430\u043d\u044b \u043e\u0448\u0438\u0431\u043a\u0430\u043c\u0438 \u0432 \u043e\u0431\u0440\u0430\u0431\u043e\u0442\u0447\u0438\u043a\u0430\u0445 \u043c\u0430\u043a\u0441\u0438\u043c\u0430\u043b\u044c\u043d\u043e\u0433\u043e \u0440\u0430\u0437\u043c\u0435\u0440\u0430 \u0431\u043b\u043e\u043a\u0430 \u0434\u0430\u043d\u043d\u044b\u0445 \u0432 TCP-\u043f\u0430\u043a\u0435\u0442\u0435 (MSS, Maximum segment size) \u0438 \u043c\u0435\u0445\u0430\u043d\u0438\u0437\u043c\u0430 \u0432\u044b\u0431\u043e\u0440\u043e\u0447\u043d\u043e\u0433\u043e \u043f\u043e\u0434\u0442\u0432\u0435\u0440\u0436\u0434\u0435\u043d\u0438\u044f \u0441\u043e\u0435\u0434\u0438\u043d\u0435\u043d\u0438\u0439 (SACK, TCP Selective Acknowledgement). CVE-2019-11477 (SACK Panic) […]<\/p>\n","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[702],"tags":[],"class_list":["post-35396","post","type-post","status-publish","format-standard","hentry","category-news"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\n","aioseo_head_json":{"title":"\ud83e\udd47Zranitelnosti v TCP z\u00e1sobn\u00edc\u00edch Linux a FreeBSD, vedouc\u00ed k vzd\u00e1len\u00e9mu odm\u00edtnut\u00ed slu\u017eby | ProHoster","description":"Spole\u010dnost Netflix odhalila n\u011bkolik 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